1. Field of the Invention
The present invention relates to computer fans, and particularly to a circuit for controlling rotation speed of a computer fan.
2. Description of Related Art
A computer system includes a motherboard with various chips such as a central processing unit (CPU) mounted thereon, a storage device such as a hard disc, and input/output devices. Many of these devices generate heat when the computer system is operating, particularly the CPU. If the heat generated from the CPU is not dissipated in a timely fashion, it may damage the CPU or even the computer system.
Typically, a sensor is programmed to be used as a temperature detector for detecting the temperature of the CPU. A computer fan is used to facilitate removal of heat to keep the temperature of the CPU within a safe temperature range. A fan controller is provided to adjust the fan speed to be more energy efficient while still providing enough heat dissipation. Two common kinds of computer fans are 3-pin fans and 4-pin fans. The fan speed of a 3-pin fan can be adjusted by changing a voltage signal (power signal) input to the 3-pin fan. The fan speed of a 4-pin fan, can be adjusted by a pulse-width modulation (PWM) signal controlled by a basic input/output system (BIOS) of the motherboard directly to the 4-pin fan.
With a 3-pin fan motherboard, a 3-pin fan is connected to the motherboard by a 3-pin header mounted on the motherboard, and a 3-pin fan controller is provided to supply the voltage signal to the 3-pin fan for adjusting the rotation speed of the 3-pin fan. With a 4-pin fan motherboard, a 4-pin fan is connected to the motherboard by a 4-pin fan header mounted on the motherboard, and a 4-pin fan controller is provided to supply the PWM signal to the fourth pin of the 4-pin fan for adjusting the rotation speed of the 4-pin fan. In theory, the 3-pin fan can be connected to the 4-pin fan motherboard by the 4-pin header. However, the 3-pin fan cannot be controlled by the 4-pin fan controller because the 3-pin fan does not have the fourth pin and cannot receive the PWM signal. Therefore, the CPU may be damaged because the heat may not be dissipated properly.
What is needed is a circuit for adjusting the rotation speed of a computer fan whether the computer fan is a 3-pin fan or a 4-pin fan.